Matthew McConaughey has revealed it was a question from his then four-year-old son that ultimately convinced him to marry Camila Alves

Matthew said: "I'm going through my head, 'You're f****** four, dude'.

"I sat there. I was like, 'It's a great question, but I mean, we're not married. When you get married, you switch your name'."

Matthew recalled Levi listened intently before asking his father whether he was afraid of getting married.

He added: "I was like, 'Yeah, I guess I am'."

The actor said he then turned to his pastor for guidance.

He added: "My pastor goes, 'Let me just ask you this, Mr Risk Taker. What's the bigger risk? Carrying on like you're going and it's going well, or taking the deeper dive into the sacramental covenant of marriage?'"

He also sought advice from "elder men who had long-term relationships, who were married for decades", admitting to his pastor marriage felt like "the bigger risk".

Matthew and Camila first met at a Los Angeles nightclub in 2006 and confirmed their relationship a year later.

Camila gave birth to their first child, Levi, on 7 July 2008.

Their daughter Vida followed in 2010, and a year later Matthew proposed.

The couple married in 2012, welcoming their third child, Livingston, later that year.

Matthew also spoke warmly of Camila in the interview, crediting her for her support throughout their marriage.

He also shared insights from his new book, Poems and Prayers, released on 16 September.

One entry, titled "The best thing you can / do for your / marriage," reflects on how the couple downsized their bed to strengthen their bond.

Matthew said in an interview with Fox News Digital: "I wake up one morning... I'm looking over there and Camila's like a football field away man.

"Then you go to bed at night, like you want to snuggle up and... 'Well, we've got to cover you up. Come about 12 feet and I'll come 12 feet'."

Realising the distance was harming their intimacy, Matthew added: "Get rid of that son of a b****. So we got a queen size where we're shoulder to shoulder. I'm telling you, it's good for your marriage."